Summary: We have conducted studies to identify cytokines or their antagonists (anti-cytokine antibodies or soluble cytokine receptors) capable of inhibiting HIV replication in human macrophages (MO) or T cells. Subsequent to showing that HIV-infected MO produce high levels of M-CSF and MIP-1a, which enable an HIV/MO reservoir to be established, we found that antagonists to M-CSF inhibit HIV replication and reduce production of MIP-1a when added to infected MO in vitro. These M-CSF antagonists may have clinical benefit as therapies for HIV by blocking production of virus by MO, reducing chemokine recruitment of HIV susceptible cells, and preventing establishment/maintenance of HIV-infected MO reservoirs in vivo (JI 2000). The lymphokine IL-2, used for restoration of CD4+ T cells in AIDS patients, was reported to increase M-CSF in human monocytes and cause a transient burst of HIV mRNA in plasma after administration. We asked if MO were the source of released HIV and found that exposure of MO to IL-2 prior to HIV infection in vitro leads to a dramatic decrease in virus replication, which correlates with an IL-2-induced decrease of CD4 and CCR5 expression. Production of M-CSF was not enhanced, suggesting that IL-2 may be beneficial in preventing MO infection, as well as restoring T cell function (AIDS 1998). Interferon-alpha (IFN-a) species differ in their ability to inhibit HIV replication in vitro, which may correlate with the varying therapeutic effects. We found that IFN-a species are effective at inhibiting HIV-1 replication in human MO, but show considerable variation in T cells that parallels cellular tropism (monocyte vs. T cell tropic). No correlation existed between antiviral and antiproliferative activity; modulation of CD4/CCR5/CXCR4 expression on MO and T cells was also not observed. Future studies will determine whether the inhibitory capacity of various species of IFN-a depends on the chemokine co-receptor, rather than the cell type infected with HIV, and whether this contributes to the toxicities associated with IFN-a therapy in HIV disease. NK cells are the first line of defense against virus-infected cells and produce cytokines that are biologically active on MO. We found that NK cells produce a novel factor which prevents HIV-1 replication following virus entry in MO, but not T cells. Partial purification indicates that the inhibitory factor(s) is approximately 10 kD with a pI of 8-10, similar to chemokines. The ability of this factor to inhibit replication of HIV, and not virus entry, and the failure of antibodies to beta chemokines to reverse the inhibition suggest that this NK cell factor is unique and may play a role in the regulation of HIV-1 expression in human MO. More recent studies focus on the identification of molecules distinct from CD4, CCR5 and CXCR4, that are involved in HIV entry. Our intent is to identify agents that target these structures and prevent fusion of the HIV envelope with the cell membrane and/or delivery of the viral capsid into the cytoplasm. We will also determine whether such inhibitors can cause deterimental effects due to modulation of cell signalling and/or cytokine production.